Tap my phone, why don't you?

A few years ago, just about everyone on the left worried about telephone-tapping. Some of our suspicions were confirmed by rogue agents such as Peter Wright, but it's a long time since I've heard anyone express the kind of fears that were routine when Baroness Thatcher was Prime Minister. This may be because we have got used to the idea that mobile phones and email are not secure, but I don't think we have fully realised what this implies in the context of an overwhelming imperative to combat international terrorism.

A few years ago, just about everyone on the left worried about telephone-tapping. Some of our suspicions were confirmed by rogue agents such as Peter Wright, but it's a long time since I've heard anyone express the kind of fears that were routine when Baroness Thatcher was Prime Minister. This may be because we have got used to the idea that mobile phones and email are not secure, but I don't think we have fully realised what this implies in the context of an overwhelming imperative to combat international terrorism.

When the Home Secretary, Charles Clarke, got up last week to outline new laws to permit indefinite house arrest for terrorist suspects, his announcement coincided with the release of the four remaining British detainees at Guantanamo Bay. They were arrested on arrival in Britain and then released without charge, a highly unsatisfactory situation that certainly did not amount to clearing their names, as their families wanted. On Friday, the Americans published details of the allegations against them.

I don't believe every single person detained at Guantanamo Bay is innocent. I oppose detention without trial and I believe torture is always wrong, but some young men are attracted to Islamic extremism and a minority have embarked on illegal actions as a consequence. As I understand it, the US has evidence against some of the Guantanamo detainees, obtained from intelligence sources, but does not want to produce it in open court.

Many of us do not trust Western intelligence agencies, especially after the fiasco of the non-existent weapons of mass destruction in Iraq. Some of the material they collect is little better than gossip but the one area in which such objections have less force is electronic surveillance, which makes it all the odder that Mr Clarke has ruled out the use in court of information obtained through telephone intercepts. Publishing extracts last week from a review commissioned by the Prime Minister, Mr Clarke revealed its puzzling conclusion that the use of intercepts would secure "a modest increase" in convictions of serious criminals, but not terrorists - a proposition challenged by David Bickford, former chief legal adviser to MI5 and MI6.

Mr Bickford stated categorically that cases had been lost because of a failure to use intercepts and that "lives could be saved" if such material was admissible. So why is the Government adamant that alone in western Europe (except for Ireland) it won't allow the one type of evidence from intelligence agencies that has some factual basis? Back to Mr Clarke, whose remarks included the assertion that the benefits of using phone-tap evidence did not outweigh "the serious risks" for intercepting agencies. This may be the case with intelligence from human sources and I can see that governments of democratic countries might be wary of admitting that evidence was obtained under torture, whether at Guantanamo Bay or by unsavoury allies. (The former British ambassador to Uzbekistan, Craig Murray, protested in a secret memo about Britain's acceptance of such material.)

So what is the "risk" Mr Clarke talks about? I suspect the Government does not want to admit how widespread its covert surveillance already is or how much our security services rely on US agencies. Technological developments mean that the British system of having to apply for individual warrants before tapping phones is laughably antiquated, and I'm sure American anti-terror agencies have no such scruples.

This theory was confirmed by an unnamed government minister who told The Times that the security services are worried that "the more this is known about, the more people will get wise to the possibility of their phones being tapped". Perfectly true, and I don't discount the civil liberties implications of electronic surveillance by our own government and its allies. My point, though, is that they are already doing it. The worst of all worlds is a de facto police state in which people can be held under house arrest for years because ministers do not want to reveal the source of evidence against them.